Pulsed fuel-oxygen burner and method for rotatable workpieces

ABSTRACT

An apparatus for applying heat to a rotatable workpiece is disclosed. A rotating lathe is provided for mounting a workpiece, for example a quartz tube, thereto so as to enable rotation of the workpiece. At least one translatable burner is coupled to a fuel source and an oxygen source for producing a flame. The burner is directed such that flame impinges upon the workpiece mounted on the rotating lathe. A first pulse control valve is coupled to and positioned between the translatable burner and the fuel source. A second pulse control valve is coupled to and positioned between the translatable burners and the oxygen course. The first and second pulse control valves are pulsed at a predetermined frequency to prevent the formation of a steady thermal boundary layer about the workpiece to improve the rate of heat transfer between the flame and the workpiece.

BACKGROUND OF THE INVENTION

This invention relates generally to fuel-oxygen burners and morespecifically to pulsed fuel-oxygen burners for rotatable workpieces.

High-purity quartz tubes are currently produced for use in the siliconchip processing industries. One method of manufacturing large outsidediameter quartz tubes, for example, between about 300 mm to about 500 mmoutside diameter quartz tubes, is to resize smaller diameter quartztubes, for example, quartz tubes having an outside diameter of less thanabout 250 mm.

One method of performing this resizing operation is analogous toglass-blowing. A quartz tube is mounted horizontally on a rotatinglathe. The interior of the quartz tube is slightly pressurized, whilethe outside of the quartz tube is heated by natural gas-oxygen jetflames, which jet flames impinge upon the outside of the rotating quartztube. The burners are first positioned at one end of the quartz tube andare slowly translated down the length of the quartz tube. The heat fromthe impinging flames soften the quartz, thus allowing the tube to expanddue to the internal pressure. This quartz tube is rotated to maintain acircular cross-section and to distribute the heat from the flames evenlyaround the circumference of the quartz tube.

A conventional process typically increases the diameter of a quartz tubeby about 50 mm with a single pass of the burners, which pass may requireup to about 45 minutes, depending on the length of the tube. Largerdiameter increases are achieved by making multiple passes of the burnersdown the length of a tube.

One drawback of this method of resizing is the large amount of naturalgas and oxygen consumed by the burners. The cost of resizing a quartztube can be as high as $30/lb. of quartz, mostly comprising the cost ofthe natural gas and oxygen. This high cost is due, in part, to lowefficiency of transferring heat from the burning natural gas-oxygen jetto the rotating quartz tube. Improving heat transfer from the burningnatural gas oxygen jets to the rotating quartz tube could result insubstantial fuel and oxygen cost savings. Additionally, increasing therate of heat transfer from the flame to the tube could reduce processingtime and increase productivity.

Accordingly, there is a need in the art for an improved fuel-oxygenburner and application for quartz tube resizing.

SUMMARY OF THE INVENTION

An apparatus for applying heat to a rotatable workpiece is disclosed. Arotating lathe is provided for mounting a workpiece, for example aquartz tube, thereto so as to enable rotation of the workpiece. At leastone translatable burner is coupled to a fuel source and an oxygen sourcefor producing a flame. The burner is directed such that the flameimpinges upon the workpiece mounted on the rotating lathe. A first pulsecontrol valve is coupled to and positioned between the translatableburner and the fuel source. A second pulse control valve is coupled toand positioned between the translatable burners and the oxygen source.The first and second pulse control valves are pulsed at a predeterminedfrequency to prevent the formation of a steady thermal boundary layerabout the workpiece to improve the rate of heat transfer between theflame and the workpiece.

BRIEF DESCRIPTION OF THE DRAWINGS

The FIGURE is a schematic, cross-sectional, side-elevational view of oneembodiment of the instant invention.

DETAILED DESCRIPTION OF THE INVENTION

An apparatus 10 for applying heat to a rotatable workpiece 12, typicallya quartz tube, is shown in FIG. 1.

Apparatus 10 typically comprises a rotating lathe 14 to mount arespective workpiece 12 to. Rotating lathe 14, when enabled to do so,rotates in the general direction of arrow A, and workpiece 12, whichworkpiece 12 is mounted to lathe 14, also rotates in the generaldirection of arrow A.

At least one translatable burner 16 is coupled to a fuel source 18 andan oxygen source 20 for producing a flame 22. Flame 22 is directed toimpinge upon workpiece 12 when workpiece 12 is mounted on rotating lathe14.

A first pulse control valve 24 is coupled to and disposed between atlast one translatable burner 16 and fuel source 18. A second pulsecontrol valve 26 is coupled to and disposed between at least onetranslatable burner 16 and oxygen source 20.

In accordance with one embodiment of the instant invention, first andsecond pulse control valves 24, 26 are pulsed at a predeterminedfrequency to prevent the formation of a steady thermal boundary layerabout an impinged upon workpiece 12 to improve the rate of heat transferbetween flame 22 and workpiece 12.

As discussed above, workpiece 12 is typically a quartz tube. Quartz tube12 is horizontally mounted on rotating lathe 14 to be rotated about acentral axis 28. The interior of quartz tube 12 is typically pressurizedvia a pressure source 30, for example, a nitrogen purge. The outside ofthe rotating quartz tube 12 is heated by flame 22, which flame 22impinges upon the outside of quartz tube 12.

At least one translatable burner 16 is typically positioned adjacent afirst end 32 of quartz tube 12 and is slowly translated along path "B"to a second end 34 of quartz tube 12 and back to first end 32, or untila respective operation is completed. The overall length (L) of quartztube 12 is typically in the range between about 3 to about 10 feet.

A typical operation to be performed on apparatus 10 is resizing quartztube 12 from a first outside diameter (D₁), typically in the rangebetween about 200 mm to about 250 mm, to a second outside diameter (D₂),typically in the range between about 300 mm to about 500 mm.

The heat from the impinging flame(s) 22 softens quartz tube 12, allowingquartz tube 12 to expand due to the internal pressure provided bypressure source 30. Quartz tube 12 is rotated generally in the directionof arrow "A" by rotating lathe 14 to maintain a generally circularcross-section and to distribute the heat from flame(s) 22 evenly aroundthe circumference of quartz tube 12.

As discussed above, at least one translatable burner 16 is typicallyslowly translated generally along path "B". In one embodiment, the rateof translation of at least one translatable burner 16 is in the rangebetween about 0.5 in/min to about 2.0 in/min.

As discussed above, first and second pulse control valves 24, 26 arepulsed at a predetermined frequency to prevent the formation of a steadythermal boundary layer about quartz tube 12 to improve the rate of heattransfer between flame 22 and quartz tube 12. In one embodiment of theinstant invention, first and second pulse control valves 24, 26 arepulsed at a frequency in the range between about 75 Hz. to about 150Hz., and preferably at about 100 Hz. In one embodiment, first pulsecontrol valve and second pulse control valve 24, 26 are synchronized sothat each pulse control valve 24, 26 pulses substantiallysimultaneously.

In one embodiment of the instant invention, at least one translatableburner 16 comprises a first and a second translatable burner axiallyaligned and oppositely directed so as to each direct an impinging flame22 upon a workpiece 12, disposed therebetween, as shown in FIG. 1. Inthis embodiment, apparatus 10 comprises two pulse control valves 24coupled to and disposed between respective translatable burners 16 andfuel source 18 and two pulse control valves 26 coupled to an disposedbetween respective translatable burners 16 and oxygen source 20.

Each of the pulse valves 24, 26 are pulsed at a predetermined frequencyto prevent the formation of a steady thermal boundary layer about animpinged upon workpiece 12 to improve the rate of heat transfer betweenflames 22 and workpiece 12. In one embodiment, all four pulse controlvalves 24, 26 are pulsed at a frequency in the range between about 75Hz. to about 150 Hz. and preferably at about 100 Hz. In anotherembodiment, all four pulse control valves 24, 26 are synchronized sothat each pulse control valve pulses substantially simultaneously.

While only certain features of the invention have been illustrated anddescribed, many modifications and changes will occur to those skilled inthe art. It is, therefore, to be understood that the appended claims areintended to cover all such modifications and changes as fall within thetrue spirit of the invention.

We claim:
 1. An apparatus for applying heat to a rotatable workpiece,said apparatus comprising:a rotating lathe for mounting a workpiecethereto so as to enable rotation thereof; at least one translatableburner coupled to a fuel source and an oxygen source for producing aflame directed to impinge upon a workpiece mounted upon said rotatinglathe; a first pulse control valve coupled to and disposed between saidat least one translatable burner and said fuel source; and a secondpulse control valve coupled to and disposed between said at least onetranslatable burner and said oxygen source; wherein said first andsecond pulse control valves are pulsed at a predetermined frequency toprevent the formation of a steady thermal boundary layer about saidworkpiece to improve the rate of heat transfer therebetween.
 2. Anapparatus in accordance with claim 1, wherein said workpiece is a quartztube.
 3. An apparatus in accordance with claim 2, wherein said quartztube is internally pressurized.
 4. An apparatus in accordance with claim2, wherein an outside diameter of said quartz tube is in the rangebetween about 250 mm to about 500 mm.
 5. An apparatus in accordance withclaim 2, wherein said apparatus is utilized to resize a quartz tubehaving an outside diameter in the range between about 200 mm to about250 mm to a quartz tube having an outside diameter in the range betweenabout 300 mm to about 500 mm.
 6. An apparatus in accordance with claim2, wherein said quartz tube has a length in the range between about 3 toabout 10 feet.
 7. An apparatus in accordance with claim 6, wherein saidat least one translatable burner impinges said flame upon a first end ofsaid quartz tube and translates said flame along the length of saidquartz tube.
 8. An apparatus in accordance with claim 1, wherein said atleast one translatable burner translates at a rate between about 0.5in./min. to about 2.0 in./min.
 9. An apparatus in accordance with claim1, wherein said first pulse control valve and said second pulse controlvalve are pulsed at a frequency in the range between about 75 Hz. toabout 150 Hz.
 10. An apparatus in accordance with claim 1, wherein saidfirst pulse control valve and said second pulse control valve are pulsedat a frequency of about 100 Hz.
 11. An apparatus in accordance withclaim 1, wherein said first pulse control valve and said second pulsecontrol valve are synchronized so that both pulse control valves pulsesubstantially simultaneously.
 12. An apparatus in accordance with claim1, wherein said at least one translatable burner comprises a first and asecond translatable burner axially aligned and oppositely directed so asto each direct an impinging flame upon a workpiece disposedtherebetween.
 13. An apparatus in accordance with claim 12, furthercomprising:a third pulse control valve coupled to and disposed betweensaid second translatable burner and said fuel source; and a fourth pulsecontrol valve coupled to and disposed between said second translatableburner and said oxygen source; wherein said third and fourth pulsecontrol valves are pulsed at a predetermined frequency to prevent theformation of a steady thermal boundary layer about an impinged uponworkpiece to improve the rate of heat transfer therebetween.
 14. Anapparatus in accordance with claim 13 wherein said pulse control valvesare pulsed at a frequency in the range between about 75 Hz. to about 150Hz.
 15. An apparatus in accordance with claim 13 wherein said pulsecontrol valves are pulsed at frequency of about 100 Hz.
 16. An apparatusin accordance with claim 13, wherein said pulse control valves aresynchronized so that each pulse control valve pulses substantiallysimultaneously.
 17. A method of applying heat to a workpiece comprisingthe method steps of:rotating a workpiece about a central axis;translating an impinging flame relative to a length of said centralaxis; and pulsing said impinging flame to prevent the formation of asteady thermal boundary layer about said workpiece to improve the rateof heat transfer between said flame and said workpiece, wherein saidstep of translating an impinging flame utilizes at least onetranslatable burner coupled to a fuel source and an oxygen source forproducing said impinging flame.
 18. A method in accordance with claim17, wherein said step of rotating a workpiece utilizes a rotating lathe.19. A method in accordance with claim 17, wherein said step of pulsingsaid impinging flame utilizes a first pulse control valve coupled to anddisposed between said at least one translatable burner and said fuelsource and a second pulse control valve coupled to an disposed betweensaid at least one translatable burner and said oxygen source, whereinsaid first and second pulse control valves are pulsed at a predeterminedfrequency.
 20. A method in accordance with claim 17, wherein saidworkpiece is a quartz tube.
 21. A method in accordance with claim 20,wherein said quartz tube is internally pressurized.
 22. A method inaccordance with claim 20, wherein an outside diameter of said quartztube is in the range between about 250 mm to about 500 mm.
 23. A methodin accordance with claim 20, wherein said method is utilized to resize aquartz tube having an outside diameter in the range between about 200 mmto about 250 mm to a quartz tube having an outside diameter in the rangebetween about 300 mm to about 500 mm.
 24. A method in accordance withclaim 20, where said length of said quartz tube is in the range betweenabout 3 to about 10 feet.
 25. A method in accordance with claim 17wherein said step of translating an impinging flame is completed at arate between about 0.5 in./min. to about 2.0 in./min.
 26. A method inaccordance with claim 19, wherein said first pulse control valve andsaid second pulse control valve are pulsed at a frequency in the rangebetween about 75 Hz. to about 150 Hz.
 27. A method in accordance withclaim 19, wherein said first pulse control valve and said second pulsecontrol valve are pulsed at a frequency of about 100 Hz.
 28. A method inaccordance with claim 19 wherein said first pulse control valve and saidsecond pulse control valve are synchronized so that each pulse controlvalve pulses substantially simultaneously.
 29. A method in accordancewith claim 17, wherein said at least one translatable burner comprises afirst and a second translatable burner axially aligned and oppositelydirected so as to each direct an impinging flame upon a workpiecedisposed therebetween.
 30. A method in accordance with claim 20, whereinsaid step of pulsing said impinging flame utilizes a first pulse controlvalve coupled to and disposed between said first translatable burner andsaid fuel source, a second pulse control valve coupled to and disposedbetween said first translatable burner and said oxygen source, a thirdpulse control valve coupled to and disposed between said secondtranslatable burner and said fuel source and a fourth pulse controlvalve coupled to and disposed between said second translatable burnerand said oxygen source, wherein said control valves are pulsed at apredetermined frequency.
 31. A method in accordance with claim 30,wherein said pulse control valves are pulsed at a frequency in the rangebetween about 75 Hz. to about 150 Hz.
 32. A method in accordance withclaim 30, wherein said pulse control valves are pulsed at a frequency ofabout 100 Hz.
 33. A method in accordance with claim 30, wherein saidpulse control valves are synchronized so that each pulse control valvepulses substantially simultaneously.